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Writing to a AT28 from Collapse OS
Goal
Write in an AT28 EEPROM from within Collapse OS so that you can have it update itself.
Gathering parts
- A RC2014 Classic
- An extra AT28C64B
- 1x 40106 inverter gates
- Proto board, RC2014 header pins, wires, IC sockets, etc.
Building the EEPROM holder
The AT28 is SRAM compatible so you could use a RAM module for it. However, there is only one RAM module with the Classic version of the RC2014 and we need it to run Collapse OS.
You could probably use the 64K RAM module for this purpose, but I don't have one
and I haven't tried it. For this recipe, I built my own module which is the same
as the regular ROM module but with WR wired and geared for address range
0x2000-0x3fff.
If you're tempted by the idea of hacking your existing RC2014 ROM module by
wiring WR and write directly to the range 0x0000-0x1fff while running it,
be aware that it's not that easy. I was also tempted by this idea, tried it,
but on bootup, it seems that some random WR triggers happen and it corrupts
the EEPROM contents. Theoretically, we could go around that by putting the AT28
in write protection mode, but I preferred building my own module.
I don't think you need a schematic. It's really simple.
Building the binary
The binary from the base recipe has almost all it needs to write to EEPROM. The
only thing it needs is the AT28 driver from B590. You could add it to the
xcomp unit and rebuild, but the driver is so tiny, you're probably better off
loading it at runtime.
If your system has mass storage, it's as easy as a LOAD. If it doesn't, you
can use /tools/exec to send blk/591 to the RC2014.
Writing contents to the AT28
The driver provides AT28! which can be plugged in adev's A!*.
First, upload your binary to some place in memory, for example a000. To do so,
run this from your modern computer:
./upload <tty device> a000 <filename>
Then, activate AT28! with ' AT28! A!* ! and then run
0xa000 0x2000 <size-of-bin> AMOVE. AT28! checks every byte for integrity,
so it there's no error, you should be fine. Your content is now on the EEPROM!
Why not upload content directly to 0x2000 after having activated AT28!?
Technically, you could. It was my first idea too. However, at the time of this
writing, I always get weird mismatch errors about halfway through. Maybe that
the ACIA interrupt does something wrong...